Combined cycle plant, device for controlling said plant, and method for starting up said plant

ABSTRACT

In a combined cycle plant, a device for controlling a combined cycle plant, and a method for starting up a combined cycle plant, the time for starting up the combined cycle plant can be shortened by providing: a gas turbine having a compressor, a combustor, and a turbine; a heat recovery steam generator for generating steam by means of the exhaust heat of exhaust gas from the gas turbine. A steam turbine is driven by the steam generated by the heat recovery steam generator; and a control device is configured to set a standby load for the gas turbine during a start-up continuously to change in accordance with a change in metal temperature of the steam turbine.

TECHNICAL FIELD

The present invention relates to a combined cycle plant including a gasturbine, a heat recovery steam generator, and a steam turbine; a devicefor controlling a combined cycle plant; and a method for starting up acombined cycle plant.

BACKGROUND ART

In combined cycle power generation, first of all, a gas turbine isdriven using natural gas or the like as fuel, thereby carrying out thefirst power generation. Next, a heat recovery steam generator recoversexhaust gas of the gas turbine and generates steam. Then, a steamturbine is driven by means of the steam, thereby carrying out the secondpower generation. Combined cycle plants are power generation plants forexecuting the combined cycle power generation.

When a combined cycle plant is started up, a standby load for the gasturbine is set in accordance with a metal temperature of the steamturbine. For example, when the metal temperature of the steam turbine isequal to or lower than 200° C., a cold start-up is conducted. Thestandby load for the gas turbine is set to 10% and the gas turbine isstarted up. Meanwhile, when the metal temperature of the steam turbineis equal to or higher than 400° C., a hot start-up is conducted. Thestandby load for the gas turbine is set to 30% and the gas turbine isstarted up. In addition, when the metal temperature of the steam turbineis within a range from 200° C. to 400° C., the standby load for the gasturbine is set to 20% and the gas turbine is started up. Then, after thegas turbine is started up and a set standby load is retained thereon,when steam generated by means of exhaust gas reaches a predeterminedtemperature and predetermined pressure, the steam is supplied to thesteam turbine, and the load on the gas turbine is increased. Morespecifically, when a mismatch between the steam temperature in an inletof the steam turbine derived out from the temperature and the pressureof steam on an outlet side of the heat recovery steam generator, and themetal temperature of the steam turbine is reduced, and when a conditionthat the degree of superheat is sufficiently ensured is satisfied, steamstarts to be supplied to the steam turbine.

Incidentally, there are demands for starting up a combined cycle plantat a standstill in an early stage and supplying electric power. Here, agas turbine alone is capable of increasing the load at a relatively highload increasing rate. However, in a steam turbine, due to therestriction of thermal stress, the load is required to be increased at aload increasing rate lower than that in the gas turbine. That is, in thecombined cycle plant, even though the load can be increased to a standbyload for the gas turbine relatively quickly, the loads on both the gasturbine and the steam turbine are required to be increased at a lowspeed after steam starts to be supplied to the steam turbine.Accordingly, compared to a case of the gas turbine alone, it takes timeto increase the load. Thus, the smaller the standby load for the gasturbine, the larger a load zone through which the loads on the gasturbine and the steam turbine are simultaneously increased. Therefore,the time for increasing the load on the entire combined plant is furtherlengthened.

Meanwhile, when the above-described combined cycle plants in the relatedart are started up, the standby load for the gas turbine with respect toa metal temperature range of the steam turbine is fixed for eachstart-up mode. Therefore, the standby load for the gas turbine changesat the border between the metal temperature ranges of the steam turbine.For example, when the metal temperature of the steam turbine is 195° C.,a cold start-up is conducted, and the standby load for the gas turbineis set to 10%. When the metal temperature of the steam turbine is 205°C., a warm start-up is conducted, and the standby load for the gasturbine is set to 20%. In this case, although the difference between themetal temperatures of the steam turbine is 10° C., which isinsignificant, when the metal temperature of the steam turbine is 195°C., the standby load for the gas turbine is set to 10%. Thus, a slightdifference between the metal temperatures of the steam turbine makes thestandby load for the gas turbine change significantly, thereby leadingto a problem in that the time for starting up the combined cycle plantis lengthened.

In addition, when the above-described combined cycle plants in therelated art are started up, an increasing load rate of the steam turbineduring a start-up is fixed for each start-up mode. Therefore, theincreasing load rate of the steam turbine changes at the border betweenthe metal temperature ranges of the steam turbine. For example, when themetal temperature of the steam turbine is 195° C., a cold start-up isconducted, and the increasing load rate is set to be relatively low.When the metal temperature of the steam turbine is 205° C., a warmstart-up is conducted, and the increasing load rate is set to berelatively high. In this case, although the difference between the metaltemperatures of the steam turbine is 10° C., which is insignificant,when the metal temperature of the steam turbine is 195° C., theincreasing load rate of the steam turbine is set to be on the low side.Thus, a slight difference between the metal temperatures of the steamturbine makes the increasing load rate of the steam turbine changesignificantly, thereby leading to a problem in that the time forstarting up the combined cycle plant is lengthened and it requires time.

The present invention has been made in order to solve theabove-described problems, and an object thereof is to provide a combinedcycle plant, a device for controlling a combined cycle plant, and amethod for starting up a combined cycle plant that can shorten a timefor starting up the combined cycle plant.

SUMMARY OF THE INVENTION

In order to achieve the object, according to the present invention,there is provided a combined cycle plant including: a gas turbine thathas a compressor, a combustor, and a turbine; a heat recovery steamgenerator that generates steam by means of exhaust heat of exhaust gasfrom the gas turbine; a steam turbine that is driven by means of steamgenerated by the heat recovery steam generator; and a control deviceconfigured to set a standby load for the gas turbine during a start-upcontinuously to change in accordance with a change in metal temperatureof the steam turbine.

Accordingly, the standby load for the gas turbine during a start-up isset to an optimum value with respect to the metal temperature of thesteam turbine, so that the gas turbine is operated under a proper load.Therefore, a load zone through which the loads on the gas turbine andthe steam turbine are simultaneously increased can be reduced as much aspossible, and the time for starting up the entire combined cycle plantcan be shortened.

In the combined cycle plant of the present invention, the standby loadis a function of the metal temperature and increases in accordance witha rise of the metal temperature.

Accordingly, since the standby load is a function increasing inaccordance with a rise of the metal temperature, when the temperature ofthe steam turbine rises, the standby load for the gas turbine increases.Therefore, it is possible to start up the gas turbine under a properload and to reduce the load zone through which the loads on the gasturbine and the steam turbine are simultaneously increased.

In the combined cycle plant of the present invention, the standby loadis a function including a low temperature region and a high temperatureregion with respect to the metal temperature, and a changing rate of thestandby load with respect to the metal temperature in the lowtemperature region and that in the high temperature region are variedfrom each other.

Accordingly, the changing rate of the standby load in the lowtemperature region and the changing rate of the standby load in the hightemperature region become different from each other. Therefore, it ispossible to carry out the design suitable for the performance of theplant.

In the combined cycle plant of the present invention, the changing rateof the standby load in the high temperature region is set to be greaterthan the changing rate of the standby load in the low temperatureregion.

Accordingly, since the changing rate of the standby load in the hightemperature region is greater than the changing rate of the standby loadin the low temperature region, the standby load varies significantlywith respect to a change in metal temperature of the steam turbine inthe high temperature region. Therefore, it is possible to further reducethe load zone through which the loads on the gas turbine and the steamturbine are simultaneously increased.

In the combined cycle plant of the present invention, the standby loadis set to a constant value in a region in which the metal temperature isequal to or lower than a lower limit temperature set in advance.

Accordingly, since the standby load is set to a constant value in theregion in which the metal temperature is equal to or lower than thelower limit temperature, it is possible to simplify control overstarting up the gas turbine.

In the combined cycle plant of the present invention, the standby loadis set to a constant value in a region in which the metal temperature isequal to or higher than an upper limit temperature set in advance.

Accordingly, since the standby load is set to a constant value in theregion in which the metal temperature is equal to or higher than theupper limit temperature, it is possible to suppress generation ofthermal stress in the gas turbine.

In addition, according to the present invention, there is provided acombined cycle plant including: a gas turbine that has a compressor, acombustor, and a turbine; a heat recovery steam generator that generatessteam by means of exhaust heat of exhaust gas from the gas turbine; asteam turbine that is driven by means of steam generated by the heatrecovery steam generator; and a control device configured to set anincreasing load rate of the steam turbine during a start-up continuouslyto change in accordance with a change in metal temperature of the steamturbine.

Accordingly, the increasing load rate of the steam turbine during astart-up is set to an optimum value with respect to the metaltemperature of the steam turbine. Therefore, after the steam turbinestarts power generation, the power generating amount of the steamturbine can be increased in an early stage, and the time for starting upthe combined cycle plant can be shortened.

In the combined cycle plant of the present invention, the increasingload rate is a function of the metal temperature and increases inaccordance with a rise of the metal temperature.

Accordingly, since the increasing load rate is a function increasing inaccordance with a rise of the metal temperature, when the temperature ofthe steam turbine rises, the increasing load rate of the steam turbineincreases. Therefore, it is possible to increase the power generatingamount of the steam turbine in an early stage.

In the combined cycle plant of the present invention, the increasingload rate is a function including a low temperature region and a hightemperature region with respect to the metal temperature, and a changingrate of the increasing load rate with respect to the metal temperaturein the low temperature region and that in the high temperature regionare varied from each other.

Accordingly, the changing rate of the increasing load rate in the lowtemperature region and the changing rate of the increasing load rate inthe high temperature region become different from each other. Therefore,it is possible to carry out the design suitable for the performance ofthe plant.

In the combined cycle plant of the present invention, the changing rateof the increasing load rate in the high temperature region is set to begreater than the changing rate of the increasing load rate in the lowtemperature region.

Accordingly, since the changing rate of the increasing load rate in thehigh temperature region is greater than the changing rate of theincreasing load rate in the low temperature region, the increasing loadrate varies significantly with respect to a change in metal temperatureof the steam turbine in the high temperature region. Therefore, it ispossible to increase the power generating amount of the steam turbine inan early stage.

In the combined cycle plant of the present invention, the increasingload rate is set to a constant value in a region in which the metaltemperature is equal to or lower than a lower limit temperature set inadvance.

Accordingly, since the increasing load rate is set to a constant valuein the region in which the metal temperature is equal to or lower thanthe lower limit temperature, it is possible to simplify control over theoperation of the combined cycle plant.

In the combined cycle plant of the present invention, the increasingload rate is set to a constant value in a region in which the metaltemperature is equal to or higher than an upper limit temperature set inadvance.

Accordingly, since the increasing load rate is set to a constant valuein the region in which the metal temperature is equal to or higher thanthe upper limit temperature, it is possible to suppress generation ofthermal stress in the steam turbine caused due to a temperaturedifference between the steam temperature and the metal temperature.

In addition, according to the present invention, there is provided adevice for controlling a combined cycle plant. The combined cycle plantincludes a gas turbine, a heat recovery steam generator, and a steamturbine. The device is configured to set a standby load for the gasturbine during a start-up continuously to change in accordance with achange in metal temperature of the steam turbine.

Accordingly, the standby load for the gas turbine during a start-up isset to an optimum value with respect to the metal temperature of thesteam turbine. Therefore, the time for starting up the combined cycleplant can be shortened.

According to the present invention, there is provided a device forcontrolling a combined cycle plant. The combined cycle plant includes agas turbine, a heat recovery steam generator, and a steam turbine. Thedevice is configured to set an increasing load rate of the steam turbineduring a start-up continuously to change in accordance with a change inmetal temperature of the steam turbine.

Accordingly, the increasing load rate of the steam turbine during astart-up is set to an optimum value with respect to the metaltemperature of the steam turbine. Therefore, the time for starting upthe combined cycle plant can be shortened.

In addition, according to the present invention, there is provided amethod for starting up a combined cycle plant including a gas turbine, aheat recovery steam generator, and a steam turbine. The method includessetting during a start-up a standby load for the gas turbinecontinuously to change in accordance with a change in metal temperatureof the steam turbine.

Accordingly, the standby load for the gas turbine during a start-up isset to an optimum value with respect to the metal temperature of thesteam turbine, so that the gas turbine is operated under a proper load.Therefore, a load zone through which the loads on the gas turbine andthe steam turbine are simultaneously increased can be reduced as much aspossible, and the time for starting up the combined cycle plant can beshortened.

According to the present invention, there is provided a method forstarting up a combined cycle plant including a gas turbine, a heatrecovery steam generator, and a steam turbine. The method includessetting during a start-up an increasing load rate of the steam turbinecontinuously to change in accordance with a change in metal temperatureof the steam turbine.

Accordingly, the increasing load rate of the steam turbine during astart-up is set to an optimum value with respect to the metaltemperature of the steam turbine. Therefore, after the steam turbinestarts power generation, the power generating amount of the steamturbine can be increased in an early stage, and the time for starting upthe combined cycle plant can be shortened.

Advantageous Effects of Invention

According to the combined cycle plant, the device for controlling acombined cycle plant, and the method for starting up a combined cycleplant of the present invention, the time for starting up the combinedcycle plant can be shortened.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a schematic configuration of a combinedcycle plant of the present embodiment.

FIG. 2 is a view illustrating a schematic configuration of a device forcontrolling a combined cycle plant of the present embodiment.

FIG. 3 is a graph illustrating a gas turbine standby load with respectto a metal temperature of a steam turbine.

FIG. 4 is a graph illustrating an increasing load rate of the steamturbine with respect to a metal temperature of the steam turbine.

FIG. 5 is a graph illustrating a start-up state of the combined cycleplant.

DESCRIPTION OF EMBODIMENT

Hereinafter, with reference to the accompanying drawings, a preferableembodiment of a combined cycle plant, a device for controlling acombined cycle plant, and a method for starting up a combined cycleplant according to the present invention will be described in detail.The present invention is not limited to the embodiment. In addition, ina case of a plurality of embodiments, the embodiments are configured tobe combined together.

FIG. 1 is a view illustrating a schematic configuration of a combinedcycle plant of the present embodiment. In the present embodiment, asillustrated in FIG. 1, a combined cycle plant 10 is provided with a gasturbine 11, a heat recovery steam generator (HRSG) 12, and a steamturbine 13.

The gas turbine 11 includes a compressor 21, a combustor 22, and aturbine 23. The compressor 21 and the turbine 23 are coupled to eachother through a rotary shaft (rotor) 24 so as to be integrallyrotatable. The compressor 21 compresses air taken in through an airintake line 25. In the combustor 22, compressed air supplied from thecompressor 21 through a compressed air supply line 26 and fuel gassupplied through a fuel gas supply line 27 are mixed and combust. Theturbine 23 is driven to rotate by means of combustion gas supplied fromthe combustor 22 through a combustion gas supply line 28. A generator 29is provided so as to be coaxial with the compressor 21 and the turbine23. When the turbine 23 rotates, power generation can be carried out.

The heat recovery steam generator 12 generates steam by means of exhaustheat of exhaust gas discharged from the gas turbine 11 (turbine 23) viaan exhaust gas discharge line 31. The heat recovery steam generator 12includes a superheater 32, an evaporator 33, and an economizer 34.Exhaust gas from the gas turbine 11 introduced from a lower portion of afurnace 35 moves upward inside the heat recovery steam generator 12, andheat recovery is performed in the order of the superheater 32, theevaporator 33, and the economizer 34, thereby generating steam.

Therefore, supply water heated by the economizer 34 is sent to a steamdrum 37 through a supply water line 36, and the supply water inside thesteam drum 37 is heated while circulating between the steam drum 37 andthe evaporator 33 via a drum water falling line 38 and a drum waterrising line 39, thereby generating steam. Steam generated in the steamdrum 37 is sent to the superheater 32 via a saturated steam line 40, andis superheated by the superheater 32. The supply water line 36 isprovided with a flow regulation valve 41.

The steam turbine 13 is driven by means of steam generated by the heatrecovery steam generator 12 and has a turbine 42. A generator 43 iscoaxially coupled to the turbine 42. Steam generated by the superheater32 is supplied to the turbine 42 via a steam supply line 44. When theturbine 42 rotates, the generator 43 can carry out power generation. Thesteam supply line 44 is provided with a flow regulation valve 45.

Steam discharged from the turbine 42 is supplied to a condenser 47 via asteam discharge line 46. The condenser 47 cools the recovered steam bymeans of cooling water (sea water) and obtains condensate. The condenser47 sends the generated condensate to the economizer 34 via a condensatesupply line 48. The condensate supply line 48 is provided with acondensate pump 49.

Therefore, when the combined cycle plant 10 is operated, in the gasturbine 11, the compressor 21 compresses air and the combustor 22 causessupplied compressed air and fuel gas to be mixed and to combust. Then,the turbine 23 is driven to rotate by means of combustion gas suppliedfrom the combustor 22, and the generator 29 carries out powergeneration. In addition, exhaust gas discharged from the gas turbine 11(turbine 23) is sent to the heat recovery steam generator 12. Supplywater heated by the economizer 34 is sent to the steam drum 37 and isheated while circulating between the steam drum 37 and the evaporator33, thereby generating steam. Steam generated in the steam drum 37 issent to the superheater 32 and is superheated. The superheated steam issent to the steam turbine 13. The turbine 42 is driven to rotate bymeans of the superheated steam, and the generator 43 carries out powergeneration. The steam used in the turbine 42 is cooled by means of thecooling water and becomes condensate, and is returned to the economizer34 by the condensate pump 49.

Incidentally, in the combined cycle plant 10 having such aconfiguration, a standby load for the gas turbine 11 at the time whenbeing started up is set in accordance with the metal temperature of thesteam turbine 13. When the gas turbine 11 is started up, the heatrecovery steam generator 12 generates steam by means of exhaust gas fromthe gas turbine 11, and the steam is supplied to the steam turbine 13such that the steam turbine 13 is driven to rotate, if there is asignificant temperature difference between the temperature of the steamand the metal temperature of the steam turbine 13, a difference inthermal expansion is caused among the constituent members of the steamturbine 13, so that thermal stress acts. Therefore, when the combinedcycle plant 10 is started up, if the metal temperature of the steamturbine 13 is low, the standby load for the gas turbine 11 is set to below, and if the metal temperature of the steam turbine 13 is high, thestandby load for the gas turbine 11 is set to be high.

That is, when the combined cycle plant 10 is started up, since thestandby load for the gas turbine 11 is set in accordance with the metaltemperature of the steam turbine 13, after the gas turbine 11 is startedup, this standby load is retained. Then, the heat recovery steamgenerator 12 generates steam by means of exhaust heat of exhaust gasfrom the gas turbine 11. When the degree of superheat of the steamgenerated by the heat recovery steam generator 12 becomes higher than areference value for the degree of superheat set in advance, and when thetemperature difference between the temperature of the steam and themetal temperature of the steam turbine 13 becomes smaller than areference value for the temperature difference, the flow regulationvalve 45 is opened, and the steam generated by the heat recovery steamgenerator 12 is supplied to the steam turbine 13, thereby starting theoperation. Thereafter, the opening degree of the flow regulation valve45 is controlled and the load on the gas turbine 11 is increased, sothat the load on the steam turbine 13 is increased and the powergenerating amount of the generator 43 is increased.

As illustrated in FIG. 2, a gas turbine control unit controllingoperation of the gas turbine 11, a steam generator control unit 52controlling operation of the heat recovery steam generator 12, and asteam turbine control unit 53 controlling operation of the steam turbineare connected to a control device 50, which controls each of the controlunits 51, 52, and 53. In addition, the control device 50 controls theopening degree of the flow regulation valve 45 which regulates thesupply quantity of steam supplied from the heat recovery steam generator12 to the steam turbine 13. Moreover, there are provided a temperaturemeasuring unit 54 measuring the metal temperature of the steam turbine13, and a temperature measuring unit 55 and a pressure measuring unit 56respectively measuring the temperature and the pressure of steamgenerated by the heat recovery steam generator 12. The metal temperaturemeasured by the temperature measuring unit 54, the steam temperaturemeasured by the temperature measuring unit 55, and the steam pressuremeasured by the pressure measuring unit 56 are input to the controldevice 50.

The temperature measuring unit 54 measures the temperature of a rotor inthe steam turbine 13. For example, the temperature of a vane in thesteam turbine 13 is measured using a thermocouple, and the temperatureis adopted as the metal temperature of the steam turbine 13. In thiscase, the correlation between the temperature of the rotor and thetemperature of the vane in the steam turbine 13 may be measured inadvance through an experiment or the like, and a measurement result ofthe temperature measuring unit 54 may be corrected based on thiscorrelating value. In addition, the temperature of a casing of the steamturbine 13, the temperature of a steam supply pipe line, and the likemay be measured using temperature measuring units.

In addition, there are provided a standby load setting unit 57 whichsets a standby load for the gas turbine 11 during a start-up inaccordance with the metal temperature of the steam turbine 13, and anincreasing load rate setting unit 58 which sets an increasing load rateof the steam turbine 13 during a start-up in accordance with the metaltemperature of the steam turbine 13. The standby load setting unit 57and the increasing load rate setting unit 58 are connected to thecontrol device 50.

Then, in the present embodiment, the control device is configured to setthe standby load for the gas turbine 11 during a start-up continuouslyto change in accordance with a change in metal temperature of the steamturbine 13. That is, the standby load setting unit 57 has a map(correlation graph) for setting a standby load for the gas turbine 11continuously to change in accordance with a change in metal temperatureof the steam turbine 13.

FIG. 3 is a graph illustrating a gas turbine standby load with respectto a metal temperature of a steam turbine. Here, the standby load forthe gas turbine 11 indicates the degree of load retained on the gasturbine 11 during an operation when the heat recovery steam generator 12generates steam by means of exhaust gas of the gas turbine 11 beforesteam is supplied to the steam turbine 13 (i.e., when the gas turbine isstarted up). A gas turbine standby load P is a ratio (%) when the totalload is 100(%). As illustrated in FIG. 3, the gas turbine standby load Pwhen the gas turbine 11 is started up is a function of a metaltemperature T of the steam turbine 13 and increases in accordance with arise of the metal temperature T.

In this case, in a region A in which the metal temperature T is equal toor lower than a lower limit temperature T1 (for example, 0° C.) set inadvance, the gas turbine standby load P is set to a constant value P1(for example, 10%). In addition, in a low temperature region B in whichthe metal temperature T rises from the metal temperature T1 to a metaltemperature T2, the gas turbine standby load P is set so as tocontinuously increase from the gas turbine standby load (constant value)P1 to a gas turbine standby load P2 (for example, 15%). Moreover, in ahigh temperature region C in which the metal temperature T rises fromthe metal temperature T2 to a metal temperature T3, the gas turbinestandby load P is set so as to continuously increase from the gasturbine standby load P2 to a gas turbine standby load (constant value)P3. Then, in a region D in which the metal temperature T is equal to orhigher than the metal temperature T3 which is an upper limittemperature, the gas turbine standby load P is set to the constant valueP3 (for example, 30%).

Then, points Q1, Q2, and Q3 are each set between the regions among theregions A, B, C, and D. In the regions B and C, the gas turbine standbyload P is a linear function of the metal temperature T, and the point Q2is set between the low temperature region B of the metal temperatures T1to T2 and the high temperature region C of the metal temperatures T2 toT3. Then, the changing rate of the gas turbine standby load P in thehigh temperature region C is set to be greater than the changing rate ofthe gas turbine standby load P in the low temperature region B.

In addition, the control device 50 is configured to set the increasingload rate of the steam turbine 13 during a start-up continuously tochange in accordance with a change in metal temperature of the steamturbine 13. That is, the increasing load rate setting unit 58 has a map(correlation graph) for setting an increasing load rate of the steamturbine 13 continuously to change in accordance with a change in metaltemperature of the steam turbine 13.

FIG. 4 is a graph illustrating an increasing load rate of the steamturbine with respect to a metal temperature of the steam turbine. Here,the increasing load rate of the steam turbine 13 indicates the degree ofspeed at which the load on the steam turbine 13 increases when steam issupplied from the heat recovery steam generator 12 to the steam turbine13. The increasing load rate of the steam turbine 13 is an increasingrange of the load on the steam turbine 13 per unit time and has acorrelation with an increasing load of combined cycle power generation(power generating amount per unit time). As illustrated in FIG. 4, anincreasing load rate R of the steam turbine 13 during a start-up is afunction of the metal temperature T of the steam turbine 13 andincreases in accordance with a rise of the metal temperature T.

In this case, in the region A in which the metal temperature T is equalto or lower than the lower limit temperature T1 (for example, 0° C.) setin advance, the increasing load rate R is set to a constant value R1. Inaddition, in the low temperature region B in which the metal temperatureT rises from the metal temperature T1 to the metal temperature T2, theincreasing load rate R is set so as to continuously increase from theincreasing load rate (constant value) R1 to an increasing load rate R2.Moreover, in the high temperature region C in which the metaltemperature T rises from the metal temperature T2 to the metaltemperature T3, the increasing load rate R is set so as to continuouslyincrease from the increasing load rate R2 to an increasing load rate(constant value) R3. Then, in the region D in which the metaltemperature T is equal to or higher than the metal temperature T3 whichis the upper limit temperature, the increasing load rate R is set to theconstant value R3.

Then, points Q11, Q12, and Q13 are each set between the regions amongthe regions A, B, C, and D. In the regions B and C, the increasing loadrate R is a linear function of the metal temperature T, and the pointQ12 is set between the low temperature region B of the metaltemperatures T1 to T2 and the high temperature region C of the metaltemperatures T2 to T3. Then, the changing rate of the increasing loadrate R in the high temperature region C is set to be greater than thechanging rate of the increasing load rate R in the low temperatureregion B.

Hereinafter, a method for starting up a combined cycle plant 10 of thepresent embodiment will be described. The method for starting up acombined cycle plant 10 of the present embodiment includes settingduring a start-up a standby load for the gas turbine 11 continuously tochange in accordance with a change in metal temperature of the steamturbine 13. In addition, the method for starting up a combined cycleplant 10 of the present embodiment includes setting an increasing loadrate of the steam turbine 13 continuously to change in accordance with achange in metal temperature of the steam turbine 13.

FIG. 5 is a graph illustrating a start-up state of the combined cycleplant. As illustrated in FIGS. 2 and 5, when the combined cycle plant 10is started up, the standby load for the gas turbine 11 is set inaccordance with the metal temperature of the steam turbine 13. That is,when the metal temperature of the steam turbine 13 is input from thetemperature measuring unit 54, the control device 50 causes the standbyload setting unit 57 to set the gas turbine standby load correspondingto the metal temperature and causes the gas turbine control unit 51 tostart up the gas turbine 11. Then, with the lapse of time, a load G onthe gas turbine 11 increases, and the load G reaches the gas turbinestandby load P at a time t1. The gas turbine 11 is operated such thatthe load G is retained to be the gas turbine standby load P. The gasturbine control unit 51 controls the load on the gas turbine 11, forexample, based on the supply quantity of fuel gas.

Then, the heat recovery steam generator 12 generates steam by means ofexhaust heat of exhaust gas from the gas turbine 11. In this case, thecontrol device 50 calculates the degree of superheat of the steamgenerated by the heat recovery steam generator 12 based on the pressureof the temperature of the steam input from the temperature measuringunit 55 and the pressure measuring unit 56. The control device 50determines whether the calculated degree of superheat is higher than thereference value for the degree of superheat. In addition, the controldevice 50 estimates the steam temperature in an inlet of the steamturbine based on the temperature and the pressure of the steam generatedby the heat recovery steam generator 12, input from the temperaturemeasuring unit 55 and the pressure measuring unit 56. The control device50 determines whether the temperature difference between the estimatedsteam temperature and the metal temperature of the steam turbine 13 issmaller than the reference value for the temperature difference.

Then, at a time t2, when the degree of superheat of the steam generatedby the heat recovery steam generator 12 becomes higher than thereference value for the degree of superheat, and when the temperaturedifference between the temperature of the steam in the inlet of thesteam turbine and the metal temperature of the steam turbine 13 becomessmaller than the reference value for the temperature difference, theflow regulation valve 45 is opened and the steam generated by the heatrecovery steam generator 12 is supplied to the steam turbine 13. Then,the steam turbine 13 starts an operation by means of the steam from theheat recovery steam generator 12. In this case, the control device 50causes the increasing load rate setting unit 58 to set the increasingload rate of the steam turbine 13 corresponding to the metal temperatureand causes the steam turbine control unit 53 to operate the steamturbine 13. Then, with the lapse of time, a load S on the steam turbine13 increases, and the power generating amount of the generator 43increases. The steam turbine control unit 53 controls the load on thesteam turbine 13, for example, based on control over the opening degreeof the flow regulation valve 45, and the supply quantity of fuel gas inthe gas turbine 11.

As described above, the combined cycle plant of the present embodimentis provided with: the gas turbine 11 that has the compressor 21, thecombustor 22, and the turbine 23; the heat recovery steam generator 12that generates steam by means of exhaust heat of exhaust gas from thegas turbine 11; the steam turbine 13 that is driven by means of steamgenerated by the heat recovery steam generator 12; and the controldevice 50 configured to set the standby load for the gas turbine 11during a start-up continuously to change in accordance with a change inmetal temperature of the steam turbine 13.

Accordingly, the standby load for the gas turbine 11 during a start-upis set to an optimum value with respect to the metal temperature of thesteam turbine 13, so that the gas turbine 11 is operated under a properload. Therefore, a load zone through which the loads on the gas turbine11 and the steam turbine 13 are simultaneously increased can be reducedas much as possible, and the time for starting up the combined cycleplant 10 can be shortened.

In the combined cycle plant of the present embodiment, the gas turbinestandby load is a function of the metal temperature, and is set so as toincrease in accordance with a rise of the metal temperature.Accordingly, when the temperature of the steam turbine 13 rises, thestandby load for the gas turbine 11 increases. Therefore, it is possibleto start up the gas turbine 11 under a proper load and to reduce theload zone through which the loads on the gas turbine 11 and the steamturbine 13 are simultaneously increased.

In the combined cycle plant of the present embodiment, the gas turbinestandby load is a function including the low temperature region and thehigh temperature region with respect to the metal temperature, and thechanging rate of the standby load with respect to the metal temperaturein the low temperature region and that in the high temperature regionare varied from each other. Accordingly, the changing rate of the gasturbine standby load in the low temperature region and the changing rateof the gas turbine standby load in the high temperature region becomedifferent from each other. Therefore, it is possible to carry out thedesign suitable for the performance of the plant.

In the combined cycle plant of the present embodiment, the changing rateof the gas turbine standby load in the high temperature region is set tobe greater than the changing rate of the gas turbine standby load in thelow temperature region. Accordingly, the gas turbine standby load variessignificantly with respect to a change in metal temperature of the steamturbine 13 in the high temperature region. Therefore, it is possible tofurther reduce the load zone through which the loads on the gas turbine11 and the steam turbine 13 are simultaneously increased.

In the combined cycle plant of the present embodiment, the gas turbinestandby load is set to a constant value in a region in which the metaltemperature is equal to or lower than the lower limit temperature set inadvance. Accordingly, it is possible to simplify control over startingup the gas turbine 11.

In the combined cycle plant of the present embodiment, the standby loadfor the gas turbine 11 is set to a constant value in a region in whichthe metal temperature is equal to or higher than the upper limittemperature set in advance. It is possible to suppress generation ofthermal stress in the gas turbine 11.

In addition, in the combined cycle plant of the present embodiment, thecontrol device 50 is configured to set the increasing load rate of thesteam turbine 13 during a start-up continuously to change in accordancewith a change in metal temperature of the steam turbine 13. Accordingly,the increasing load rate of the steam turbine during a start-up is setto an optimum value with respect to the metal temperature of the steamturbine 13. Therefore, after the steam turbine 13 starts powergeneration, the power generating amount of the steam turbine 13 can beincreased in an early stage, and the time for starting up the combinedcycle plant 10 can be shortened.

In the combined cycle plant of the present embodiment, the increasingload rate of the steam turbine 13 is a function of the metal temperatureand increases in accordance with a rise of the metal temperature.Accordingly, when the temperature of the steam turbine 13 rises, theincreasing load rate of the steam turbine 13 increases. Therefore, it ispossible to increase the power generating amount of the steam turbine 13in an early stage.

In the combined cycle plant of the present embodiment, the increasingload rate is a function including the low temperature region and thehigh temperature region with respect to the metal temperature, and thechanging rate of the increasing load rate with respect to the metaltemperature in the low temperature region and that in the hightemperature region are varied from each other. Accordingly, the changingrate of the increasing load rate in the low temperature region and thechanging rate of the increasing load rate in the high temperature regionbecome different from each other. Therefore, it is possible to carry outthe design suitable for the performance of the plant.

In the combined cycle plant of the present embodiment, the changing rateof the increasing load rate in the high temperature region is set to begreater than the changing rate of the increasing load rate in the lowtemperature region. Accordingly, the increasing load rate variessignificantly with respect to a change in metal temperature of the steamturbine 13 in the high temperature region. Therefore, it is possible toincrease the power generating amount of the steam turbine 13 in an earlystage.

In the combined cycle plant of the present embodiment, the increasingload rate is set to a constant value in a region in which the metaltemperature is equal to or lower than the lower limit temperature set inadvance. Accordingly, it is possible to simplify control over theoperation of the combined cycle plant 10.

In the combined cycle plant of the present embodiment, the increasingload rate is set to a constant value in a region in which the metaltemperature is equal to or higher than the upper limit temperature setin advance. Accordingly, it is possible to suppress generation ofthermal stress in the steam turbine 13 caused due to a temperaturedifference between the steam temperature and the metal temperature.

In addition, the device for controlling a combined cycle plant of thepresent embodiment is configured to set the standby load for the gasturbine 11 during a start-up continuously to change in accordance with achange in metal temperature of the steam turbine 13. Accordingly, thestandby load for the gas turbine 11 during a start-up is set to anoptimum value with respect to the metal temperature of the steamturbine. Therefore, the time for starting up the combined cycle plant 10can be shortened.

In addition, the device for controlling a combined cycle plant of thepresent embodiment is configured to set the increasing load rate of thesteam turbine 13 during a start-up continuously to change in accordancewith a change in metal temperature of the steam turbine 13. Accordingly,the increasing load rate of the steam turbine during a start-up is setto an optimum value with respect to the metal temperature of the steamturbine 13. Therefore, the time for starting up the combined cycle plant10 can be shortened.

In addition, the method for starting up a combined cycle plant of thepresent embodiment includes setting during a start-up a standby load forthe gas turbine continuously to change in accordance with a change inmetal temperature of the steam turbine. In addition, the method includessetting an increasing load rate of the steam turbine 13 continuously tochange in accordance with a change in metal temperature of the steamturbine 13. Accordingly, the time for starting up the combined cycleplant 10 can be shortened.

In the embodiment described above, the standby load for the gas turbine11 and the increasing load rate of the steam turbine 13 are set to belinear functions in each of the regions of the metal temperature of thesteam turbine 13. However, the embodiment is not limited to thisrelationship. That is, the standby load for the gas turbine 11 or theincreasing load rate of the steam turbine 13 may be a function equal toor higher than a quadratic function of the metal temperature of thesteam turbine 13.

In addition, in the embodiment described above, the standby load for thegas turbine 11 and the increasing load rate of the steam turbine 13 areset to constant values in a region in which the metal temperature T isequal to or lower than the lower limit temperature set in advance.However, the standby load and the increasing load rate may also be setto increase in accordance with a rise of the metal temperature T in thisregion, too.

In the embodiment described above, one gas turbine 11 and one steamturbine 13 are combined in the combined cycle plant 10. However, therotary shafts (rotors) thereof may be coaxial with each other or mayhave axes different from each other. In addition, a plurality of gasturbines 11 and one steam turbine 13 may be combined.

REFERENCE SIGNS LIST

-   -   10 COMBINED CYCLE PLANT    -   11 GAS TURBINE    -   12 HEAT RECOVERY STEAM GENERATOR    -   13 STEAM TURBINE    -   21 COMPRESSOR    -   22 COMBUSTOR    -   23 TURBINE    -   29, 43 GENERATOR    -   32 SUPERHEATER    -   33 EVAPORATOR    -   34 ECONOMIZER    -   37 STEAM DRUM    -   42 TURBINE    -   45 FLOW REGULATION VALVE    -   47 CONDENSER    -   49 CONDENSATE PUMP    -   50 CONTROL DEVICE    -   51 GAS TURBINE CONTROL UNIT    -   52 STEAM GENERATOR CONTROL UNIT    -   53 STEAM TURBINE CONTROL UNIT    -   54, 55 TEMPERATURE MEASURING UNIT    -   56 PRESSURE MEASURING UNIT    -   57 STANDBY LOAD SETTING UNIT    -   58 INCREASING LOAD RATE SETTING UNIT

The invention claimed is:
 1. A device for controlling a combined cycleplant, the combined cycle plant including a gas turbine, a heat recoverysteam generator, and a steam turbine, the device comprising: acontroller configured to set a standby load to continuously change inaccordance with a change in metal temperature of the steam turbine, thestandby load being a load retained on the gas turbine when the gasturbine is started up; wherein the controller is configured to: acquirethe metal temperature of the steam turbine; set the standby load basedon the metal temperature acquired, and to continuously adjust thestandby load in accordance with the change in metal temperature of thesteam turbine; and start up and drive the gas turbine such that a loadof the gas turbine reaches the standby load and the load of the gasturbine is retained on the standby load.
 2. A combined cycle plantcomprising: a gas turbine including a compressor, a combustor, and aturbine; a heat recovery steam generator configured to generate steam byexhaust heat of exhaust gas from the gas turbine; a steam turbine to bedriven by means of steam generated by the heat recovery steam generator;and the device according to claim
 1. 3. The combined cycle plantaccording to claim 2, wherein the standby load is a function of themetal temperature and increases in accordance with a rise of the metaltemperature.
 4. The combined cycle plant according to claim 3, whereinthe standby load is a function including a low temperature region and ahigh temperature region with respect to the metal temperature, and achanging rate of the standby load with respect to the metal temperaturein the low temperature region and that in the high temperature regionare varied from each other.
 5. The combined cycle plant according toclaim 4, wherein the changing rate of the standby load in the hightemperature region is set to be greater than the changing rate of thestandby load in the low temperature region.
 6. The combined cycle plantaccording to claim 2, wherein the standby load is set to a constantvalue in a region in which the metal temperature is equal to or lowerthan a lower limit temperature set in advance.
 7. The combined cycleplant according to claim 2, wherein the standby load is set to aconstant value in a region in which the metal temperature is equal to orhigher than an upper limit temperature set in advance.
 8. A combinedcycle plant comprising: a gas turbine including a compressor, acombustor, and a turbine; a heat recovery steam generator configured togenerate steam by exhaust heat of exhaust gas from the gas turbine; asteam turbine driven by steam generated by the heat recovery steamgenerator; and the device according to claim
 1. 9. The combined cycleplant according to claim 8, wherein the increasing load rate is afunction of the metal temperature and increases in accordance with arise of the metal temperature.
 10. The combined cycle plant according toclaim 9, wherein the increasing load rate is a function including a lowtemperature region and a high temperature region with respect to themetal temperature, and a changing rate of the increasing load rate withrespect to the metal temperature in the low temperature region and thatin the high temperature region are varied from each other.
 11. Thecombined cycle plant according to claim 10, wherein the changing rate ofthe increasing load rate in the high temperature region is set to begreater than the changing rate of the increasing load rate in the lowtemperature region.
 12. The combined cycle plant according to claim 8,wherein the increasing load rate is set to a constant value in a regionin which the metal temperature is equal to or lower than a lower limittemperature set in advance.
 13. The combined cycle plant according toclaim 8, wherein the increasing load rate is set to a constant value ina region in which the metal temperature is equal to or higher than anupper limit temperature set in advance.
 14. The device according toclaim 1, wherein the controller is configured to set an increasing loadrate of the steam turbine during a start-up to continuously change inaccordance with a change in metal temperature of the steam turbine. 15.A method of starting up a combined cycle plant, the combined cycle plantincluding a gas turbine, a heat recovery steam generator, and a steamturbine, and said method comprising: setting during a start-up a standbyload to continuously change in accordance with a change in metaltemperature of the steam turbine, the standby load being a load retainedon the gas turbine when the gas turbine is started up; wherein saidsetting the standby load during the start-up comprises: acquiring themetal temperature of the steam turbine; setting the standby load basedon the metal temperature acquired, and continuously adjusting thestandby load in accordance with the change in metal temperature of thesteam turbine; and starting up and driving the gas turbine such that aload of the gas turbine reaches the standby load and the load of the gasturbine is retained on the standby load.
 16. The method according toclaim 15, further comprising setting during a start-up an increasingload rate of the steam turbine to continuously change in accordance witha change in metal temperature of the steam turbine.